Forcing resits on teenagers who do not get good GCSEs in English and maths is causing "significant problems", the new head of Ofsted has argued.
Amanda Spielman said the policy, introduced in 2013, was "well intentioned" but questioned whether it was "the right way forward".
She pointed out that only a third of students managed to improve their GCSE grades in resits last year.
Ministers say they aim to develop "credible" alternatives to resits.
In 2013, the coalition government introduced a policy that said students in England who fail to get at least C grades in the two subjects should carry on studying them until the age of 18, with the aim of meeting the standard.